Local convection heat transfer coefficient flowing through tube.

[fegr fgyt]

Is it true that when fluid flow in circular tube, the local convection heat transfer coefficient decreases with distance from the inlet for both laminar and turbulent flow?

 

[racookpe1978]

You have either lamina flow, or turbulent flow in the "circular tube" - a pipe or heat exchanger tube, I presume. The local heat transfer coefficient does not greatly change from point to point down the pipe if flow/temperature/density does not change; but its film conditions AND the thus the film coefficient itself changes as the fluid conditions changes as its temperature/pressure/viscosity/heat transfer values change down the pipe.

But, because heat transfer properties of almost every fluid and gas change with temperature/pressure, usually, you MUST re-approximate the local heat transfer coefficient as temperature changes every inch/cm of the tube.

This is practically impossible, so the average of the middle of the film temperature at the middle of the tube length is chosen as "close enough".

(We don't know if your fluid is heating up, or cooling down as it goes through the tube. We don't know your fluid, its initial and final temperature, pressure, and flow rate, so we cannot answer your question even approximately.)

 

[georgeverghese]

Yes, there is one expression For N_Nu at Nre<2100, and another at 2100<Nre<1e4 where the local htc is a function of the D/L ratio. You can also see this graphically on the Colburn charts. Would guess most heat transfer texts wuld have the detailed expressions for these 2 regions.